Power efficient channel scheduling in a wireless network

ABSTRACT

A method and system for optimizing channel access scheduling for multiple wireless computing devices over a wireless network improves channel access efficiency with respect to a primary channel. An access point, or host computer, includes a host transceiver for receiving control information from the wireless computing devices over a low power channel. Upon receiving the control information, the access point applies a scheduling algorithm to schedule channel access for the wireless computing devices to transmit data over the primary communication channel. The wireless computing devices include a low power radio for receiving scheduling information via the low power channel during idle periods. When the scheduling information is received, the wireless computing device activates its primary channel network interface components to communicate data through the primary channel. When the computing device is idle, the device is configured to power down all of its components with the exception of the circuitry required to power the low power channel. As such, the low power channel is maintained in an active state for receiving scheduling information, such as an access schedule, during both idle and non-idle periods.

This application is a divisional of U.S. application Ser. No.10/124,721, filed Apr. 17, 2002, entitled: “Power Efficient ChannelScheduling in a Wireless Network”, which is herein incorporated byreference in its entirety for all that it discloses without exclusion ofany portion thereof.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to wireless computing devices,and more particularly, to power efficient channel access scheduling forwireless computing devices using multiple radios.

BACKGROUND OF THE INVENTION

Many wireless computing devices, such as laptop computers, personaldigital assistant devices, etc., may act as client devices in a wirelessnetworking environment. Often these multiple clients all communicate viathe network through shared radio frequency channels to a shared accesspoint. However, when a large number of such client devices attempt toaccess the network, this sharing of network access points often leads tocongestion and a wasting of bandwidth. Congestion often leads tocollisions in the channel between data signals and hence to delay.

To overcome these challenges, various control techniques have beenimplemented with respect to wireless networks to aid in scheduling toavoid collisions. For example, clients may engage inlisten-before-transmit (“LBT”) mechanisms, such as the CSMA-CA channelaccess mechanism, vying for space in the shared channel beforetransmitting. LBT techniques are a type of distributed coordinatedfunction. CSMA-CA is a particular Ethernet LAN access method. However,with all LBT schemes, if one client device is currently transmittingsignals (i.e. data packets) in the channel, other senders are forced toback off and wait a random amount of time before attempting accessagain. Additionally, even if the client devices detect that the networkis free, two such devices may access the channel at exactly the sametime, causing a signal collision. When this type of collision isdetected, both client devices are forced to back off and wait a randomamount of time before attempting transmission again. While the clientdevices are waiting, channel bandwidth is wasted, packet transmission isdelayed, and battery power on the client machine is wasted.

Other mechanisms exist for aiding in scheduling and avoiding collisionbetween data signals over a shared channel. Another example is apoint-coordinated function (“PCF”), which repeatedly polls the clientdevices in order to avoid collisions of signals. However, while PCFtechniques avoid the constant back and forth between the competing datasignals, the constant polling on the primary channel wastes a largeamount of bandwidth, thus making this technique highly inefficient.

While current wireless channel access techniques do produce collisionavoidance, they also waste bandwidth on the primary channel used to senddata packets because these techniques use the channel both to transmitcontrol and scheduling information and to send useful data. Distributedcoordinated functions, such as CSMA-CA, are further inefficient forreal-time data because of the forced waiting period. Real-time audiodata may no longer be useful, or sufficient, after a forced delay, suchas a 100-millisecond delay. Additionally, there is no guarantee ofchannel access by any of these techniques and there is no mechanism toassure that high priority data signals are transferred in a timelymanner.

However, if the access point knows the exact state of every client it isservicing (e.g. number of packets pending in the queue, the packetsdeadlines, and packet priorities), it can schedule each clientindependently on the channel. While researchers have attempted to buildtrue work conserving fair queuing algorithms based upon this premise,these algorithms have not been truly work conserving because part of thebandwidth on the channel is used up in transmitting control informationto the scheduler and in many cases the media-access control (MAC)protocol has to be changed. Therefore, even with such techniquesbandwidth is wasted.

Additionally, while largely avoiding signal collisions, these techniquescause inefficient use of power because they often use a high-poweredchannel to send control data in addition to useful data. A particularcomponent of a wireless device that consumes a significant amount ofpower is the network interface card (NIC), which handles the wirelesstransmission and reception of network communication data. It has beenestimated that on average, about 20% of the total power available to awireless device is dissipated as a result of the connection of a NIC, orother wireless LAN interface component. This phenomenon is due to thefact that the NIC and wireless device must be in a constant “listening”state in order to receive and transmit data via the network. Since theamount of power a battery can provide is rather limited, minimizing thepower consumption of a mobile device in order to extend its operationtime is an important consideration in the design of battery operatedwireless devices, and any communication systems involving such devices.

SUMMARY OF THE INVENTION

To address the challenges described above, a method and system aredisclosed for power efficient channel scheduling of wireless clientdevices in a wireless network using multiple radios. This method andsystem lead to optimum use of channel bandwidth and power in wirelesscomputing devices. Therefore, true work conserving algorithms can beimplemented. Such wireless computing devices include, but are notlimited to, personal data assistants (“PDAs”), cellular phones, andlaptop computers having network interface capabilities.

In accordance with an embodiment of the invention, a wireless computingdevice enables a low power control channel to exchange informationincluding control information for a network interface card (NIC), andother power consuming components of the computing device, with a hosttransceiver, referred to as a smartbrick. Initially, the low powertransceiver registers with the host transceiver, such as a hosttransceiver located at a network wireless access point. The low powertransceiver operated by the wireless computing device then sends controlinformation data signals to the host transceiver. This information maybe, but is not limited to, state information, the number of data packetsin a queue, the packet priority, and/or packet deadline. The hosttransceiver then responds by transmitting scheduling information back tothe low power transceiver. This scheduling information may include,among other things, channel access information.

Prior to receiving scheduling information from a host transceivercomponent, the high power wireless network interface components, such asassociated with an ordinary wireless NIC, are idle. Idle periods areperiods when a low power state of operation is employed by the wirelesscomputing device, or periods when no substantive network activity (e.g.,sending or receiving of data) is being engaged in by the wirelesscomputing device via its high frequency communication channel (e.g.,IEEE 802.11 based channel). After receiving the scheduling informationon the low power control channel, the full power NIC and necessarycircuitry are automatically activated consistent with the schedulinginformation. For example, in one embodiment, upon receiving channelaccess information, such as a message that the channel is free fortransmission, the NIC and other components of the wireless computingdevice are powered up. The network interface component, such as the NIC,then transmits or receives data over the high power channel.

The low power control channel is implemented via an internal or externalradio frequency (RF) transceiver component, referred to as a minibrick,which preferably operates at a low frequency (such as lower than that ofthe full power NIC) and low power level. In operation, when thecomputing device is idle, the device is configured to power downsubstantially all of its components with the exception of the circuitryrequired to power the low power transceiver. As such, the controlchannel is maintained in an active state for receiving signals duringboth idle and non-idle periods.

In accordance with another embodiment of the invention, the smartbrickis implemented as a host transceiver that operates at a host computer,or network access point, to communicate with the minibrick. The hostcomputer may also be equipped with an IEEE 802.11 based NIC forsupporting wireless communication to access the network through awireless access point (AP). The wireless AP acts as an interface to anetwork infrastructure, such as a wired enterprise LAN. When arequesting device wishes to communicate with a wireless computingdevice, it queries a server in order to determine the location andpresence of the wireless computing device. In response, the serversubmits the query to the host computer. The smartbrick operating on thehost computer receives the query from the server, and communicates withthe minibrick via the low power channel to begin scheduling andoperation of full power communications. The wireless computing devicereceives this signal and powers up the NIC and other componentsaccordingly, resulting in activation of the wireless device prior to anyactual transmission of data by the requesting device.

Additional features and advantages of the invention will be madeapparent from the following detailed description of illustrativeembodiments that proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

While the appended claims set forth the features of the presentinvention with particularity, the invention and its advantages may bebest understood from the following detailed description taken inconjunction with the accompanying drawings, of which:

FIG. 1 is a schematic diagram of an exemplary computer network withinwhich embodiments of the invention may be implemented;

FIG. 2 is a schematic diagram illustrating the architecture of anexemplary computing device in which an embodiment of the invention maybe implemented;

FIG. 3 is a schematic diagram illustrating an architecture of atransceiver component operated by a computing device for maintaining alow power control channel in an embodiment of the invention;

FIG. 4 is a schematic diagram illustrating an exemplary operatingenvironment for optimum channel scheduling through a low power controlchannel according to an embodiment of the invention;

FIG. 5 is a flowchart illustrating the operation of a host transceiverfor communicating with a wireless computing device via a low powercontrol channel according to an embodiment of the invention;

FIG. 6 is a schematic diagram illustrating an operating environment foroptimizing channel scheduling wherein the host transceiver is logicallyconnected to a host computer according to an embodiment of theinvention;

FIG. 7 is a channel diagram illustrating bi-directional communicationsin a two-channel system;

FIG. 8 a is a schematic diagram illustrating a networked environmentwherein the multiple wireless network devices vying for channel spaceare out-of-range of the wireless access point; and

FIG. 8 b is a schematic diagram illustrating a multi-hop networkoperating environment for optimizing channel scheduling when one or moreof the multiple wireless devices vying for channel space areout-of-range, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method and system for traffic handling ofcomputing devices that are capable of communicating over a wirelesslink. Wireless computing devices usable within embodiments of theinvention include, but are not limited to, personal data assistants,cellular phones, and laptop computers having wireless network interfacecapabilities. In the context of the invention, wireless communication isthe transmission of data between computing devices using radio frequency(RF) and electromagnetic waves rather than wires. To facilitate wirelesscommunication, a computing device may be equipped with a networkinterface component, such as a network interface card (NIC) thatinterfaces the device to the network. Typically, the NIC is implementedas a plug and play device that can be inserted into a network card slotof the computing device or that can be otherwise interfaced to thedevice. Alternatively, the NIC can be built integrally as part of thecircuitry of the computing device.

To facilitate wireless communication, the NIC supports a wirelessprotocol, such as pursuant to the IEEE 802.11 standard. Generalreference will be made throughout the course of this description to802.11 as a suitable protocol for facilitating wireless communicationbetween devices. However, those skilled in the art will recognize that802.11 is only one protocol for facilitating wireless communication, andthat the invention is not limited to any particular wireless protocol.Indeed, other wireless protocols may be utilized alternatively oradditionally in connection with the invention. It will also berecognized by those skilled in the art that the designation 802.11refers to other protocols within the same family, including 802.11a,802.11b or 802.11g.

An example of a networked environment in which the invention may be usedis shown in FIG. 1. The example network includes several computingdevices 20 communicating with one another over a network 30, such as theInternet, as represented in the figure by a cloud. Network 30 mayinclude one or more well-known components, such as routers, gateways,hubs, etc. and may allow the computers 20 to communicate via wiredand/or wireless media.

Referring to FIG. 2, an example of a basic configuration for a computingdevice on which the system described herein may be implemented is shown.In its most basic configuration, the computing device 20 typicallyincludes at least one processing unit 42 and memory 44 although such isnot required. Depending on the exact configuration and type of thecomputing device 20, the memory 44 may be volatile (such as RAM),non-volatile (such as ROM or flash memory) or some combination of thetwo. The most basic general configuration is illustrated in FIG. 2 bydashed line 46. Additionally, the computing device may also have otherfeatures/functionality. For example, computer 20 may also includeadditional data storage components (removable and/or non-removable)including, but not limited to, magnetic or optical disks or tape.Computer storage media includes volatile and non-volatile, removable andnon-removable media implemented in any method or technology for storageof information such as computer-readable instructions, data structures,program modules, or other data. Computer storage media includes, but isnot limited to, RAM, ROM, EEPROM, flash memory or other memorytechnology, CD-ROM, digital versatile disk (DVD) or other opticalstorage, magnetic cassettes, magnetic tape, magnetic disk storage orother magnetic storage devices, or any other medium which can be used tostore the desired information and which can be accessed by the computingdevice 20. Any such computer storage media may be part of the computingdevice 20.

The computing device 20 also preferably contains communicationconnections 48 that allow the device to communicate with other devices.A communication connection is an example of a communication medium.Communication media typically embodies readable instructions, datastructures, program modules or other data in a modulated data signalsuch as a carrier wave or other transport mechanism and includes anyinformation delivery media. By way of example, and not limitation,communication media includes wired media such as a wired network ordirect-wired connection, and wireless media such as acoustic, RF,infrared and other wireless media. The term computer readable media asused herein includes both storage media and communication media.

A computing device 20 may also have input devices such as a keyboard,mouse, pen, voice input device, touch input device, etc. Output devicessuch as a display 48, speakers, a printer, etc. may also be included.Furthermore, for wireless mobile devices, the computing device 20 ispreferably provided with a portable power source 50, such as a batterypack, fuel cell or other power module. The power source 50 acts as aprimary source of power for computations and wireless data transmissionsto be performed by the device. All the aforementioned components andfeatures are well known in the art.

The device 20 preferably supports an operating system, for examplestored in nonvolatile memory and executed by the processing unit 42 fromvolatile memory. According to an embodiment of the invention, theoperating system contains instructions for interfacing the device 20 toa full power wireless network and to a low power wireless network. Inthis manner, scheduling information usable to schedule access of thedevice 20 to the full power wireless network may be sent over the lowpower wireless network, saving device power and saving bandwidth in thefull power channel, according to the techniques to be more fullydiscussed elsewhere herein.

A device, component or group of components may be described herein as“powered up” when the relevant device, component or group of componentsis in an “ON” state of operation, e.g. operating, or at least receivingpower and immediately ready to operate, in its ordinary mode ofoperation. Conversely, when a device, component or group of componentsis described as being “powered down,” the relevant device, component orgroup of components is not operating in its ordinary mode of operation,and is not receiving power and immediately ready to operate in itsordinary mode of operation.

In accordance with an embodiment of the invention, the computing device20 is further equipped with a low power transceiver component 100 formaintaining a RF control channel, as illustrated in greater detail inFIG. 3. The low power transceiver component, referred to as a minibrick100, is comprised of various components for the receipt and transmissionof data, including a logic device 102 for controlling the operation ofthe transceiver and for affecting the operation of the computing device20 in response to various network events. Also preferably included is avoltage regulator 104 for adapting the voltage output of a low powerbattery unit 106. The low power battery unit 106 is suitable forpowering the transceiver using minimal power, and can operateindependently of the portable battery source 50. Alternatively, theprimary battery source 50 may be used to implement the same function asa low power battery unit 106. The low power transceiver 100 alsoincludes a radio frequency (RF) generator 108 for generating andproviding radio frequency signals for transmission. Other elements 109for implementing or enhancing the transceiver functions may also beincluded as part of the low power transceiver circuitry and describedelements may be altered or replaced.

Physically, the low power transceiver 100 can be implemented as aninternal component of the computing device 20, such as by integrating itwith the primary circuitry of the computing device 20, or it can beconnected to the computing device via a peripheral connection, such asan RS232 connection (e.g., the input channels 41). Also, the low powertransceiver 100 is configured to support a control channel for receivingand sending data via the radio component 108. Exemplary operatingcharacteristics for the low power transceiver 100 for implementing thelow power control channel are shown in TABLE 1.

TABLE 1 Example operational characteristics for the low powertransceiver 100. Data Rate 19.2 Kbps Modulation 00 K Voltage 3 VReceiver Current 4.5 mA Peak Radio Output Power 0.75 mWAs illustrated, the various characteristics of the low power transceiverresult in the generation of a low power, and preferably low frequencydata communication channel at 915 MHz, supporting a data rate of 19Kbps, which is substantially less than that of standard wireless NICs.Conventional NICs, such as those based on the IEEE 802.11 standard,operate at much higher data rates ranging approximately from 1–20 Mbps.Because of the higher data rates and ranges associated with standardNICs, the power consumption for powering up the standard NIC is alsohigher. The low power transceiver 100, however, requires less power tooperate, and is configured to remain active even during powered offstates of all or some of the rest of the wireless computing device 20.While not limited to the operating characteristics of TABLE 1, the lowpower transceiver is suitable for generating and receiving RF signalswithout requiring significant power usage by the device. For anexplanation of other features and aspects of the enhanced two-radionetwork device, please see U.S. patent application Ser. No. 10/124,737,entitled Reducing Idle Power Consumption in a Networked Battery OperatedDevice, filed Apr. 17, 2002, which is herein incorporated by referencein its entirety for all that it discloses.

Referring now to FIG. 4, an exemplary network environment within which awireless computing device, such as the device of FIGS. 2–3, may operateis shown in accordance with an embodiment of the invention. Theexemplary network includes a server 200, which interfaces with acomputer network 202 and manages various network resources including aBrick Server 203 and a presence server 201. The Brick Server 203 andpresence server 201 operate at the server 200 to facilitate specificnetwork tasks. In particular, the presence server maintains a list ofclients that are registered with the network server 200 in order to havetheir state of presence maintained. Presence data or information is anydata received over the network that describes the availability,proximity, location, activity level or operating state of a computingdevice or corresponding user of a device. By registering with the server200, client devices connected to the network 202 may query the presenceserver 201 to detect the presence of other devices. Similarly, the BrickServer 203 maintains and manages presence information pertaining to oneor more low power transceivers or host transceivers, which are low powertransceiver components used to implement a low frequency control channelwithin the network infrastructure. The operation of the host transceiverand low power transceiver within the network environment will bedescribed in greater detail hereinafter.

While maintaining network resources, the server 200 facilitatescommunication for one or more computing devices that communicate overthe network 202. A first client device 204 is configured to the network202 through a wired connection (e.g., T1 line, modem) or wirelessconnection. The access point 210 acts as an intermediate device betweena second client device, such as wireless computing device 220, and thenetwork 202. Additionally, logically connected to the access point 210is a host transceiver 212, which generates radio frequency signals forcommunicating with low power transceivers 100 and 102. In an alternativeembodiment of the invention, illustrated in FIG. 6, the host transceiver212 is logically connected to a host computing device configured througha wireless connection. In particular, the host computing device 206connects to the network 202 through a wireless connection 208 (e.g.,802.11 connection) to the wireless access point 210. The access point,in this embodiment, may act as an intermediate device between the hostcomputing device 206 and the network infrastructure 202. Note that theaforementioned architectures are exemplary and that any other link thatcomprises a low power RF link may be used to interface a device, such asdevices 220 and 222, to any access controlling entity, such as accesspoint 210 within the invention.

The host transceiver 212 registers with the Brick Server 203 maintainedby the server 200 in order to report its presence. When the hosttransceiver is connected to the network via a host computing device 206,as illustrated in FIG. 6, it is able to detect, when needed, theoccurrence of various network events, such as, for example, thetransmission of a message to the host computing device 206, an update topresence information maintained by the Brick Server 203, thetransmission of messages intended for transmission by the access point210, and any other statistics relative to the performance of the network202.

In accordance with an embodiment of the invention, multiple wirelesscomputing devices operating low power transceivers 100 and 102communicate with the host transceiver 212 via a low power controlchannel, as illustrated in FIG. 4. The wireless computing devices arehandheld devices 220 and 222 having wireless computing capabilities. Lowpower transceivers 100 and 102 are coupled to the wireless computingdevices 220 and 222 for providing low power, preferably low frequencycontrol channels. The low power transceivers 100 and 102 are enabled toremain powered up even during inactive or idle periods when thecomponents of the wireless computing devices 220 and 222 (other than thecircuitry required for the low power transceiver 100 and 102) are whollyor substantially powered off. Preferably, the low power transceivers 100and 102 are capable of activating the wireless computing devices 220 and222 (e.g. transferring them from an inactive or idle state to an activeor non-idle state) in response to the receipt of scheduling information,such as channel access information.

To enable either low power transceiver 100, 102 to engage incommunication over the low power control channel, the low powertransceivers 100 and 102 first register with the Brick Server 203maintained by the server 200. A user of either wireless computing device220, 222 can enable the registration process manually, such as byrunning a network application on either device 220, 222 that engages theregistration process. Alternatively, the registration process can beperformed without user intervention through a simple communicationscheme engaged in by the host transceiver 212 and either low powertransceiver 100, 102, as described below.

To determine whether a low power transceiver exists within radio rangeand requires registration, the host transceiver 212 periodicallybroadcasts beacon or detection signals indicating that the hosttransceiver is within a suitable range for engaging in communication viathe low power control channel. This periodic detection signal is sentpreferably when the host transceiver 212 is not transmitting other typesof control signals or data. When the appropriate low power transceiver100, 102 operating at the appropriate wireless computing device 220, 222detects the detection signal, the low power transceiver 100, 102generates and sends a message to the host transceiver 212 indicatingthat it is within low power radio range of the host transceiver 212.Upon receiving such a message, the host transceiver 212 determines itscapability to “manage” the relevant low power transceiver 100, 102, andreplies to the low power transceiver 100, 102 with an acknowledgementmessage when appropriate. The host transceiver's 212 ability to manage aspecific low power transceiver 100, 102 may be based on the currentsituation at the access point, including, but not limited to, the numberof clients currently vying for channel access. A responseacknowledgement is subsequently generated and sent to the hosttransceiver 212 by the low power transceiver 100, 102, which results inan association (connection or link) between the host transceiver 212 andthe relevant low power transceivers 100, 102. Having established anassociation between the host transceiver 212 and both low powertransceivers 100 and 102, the host transceiver transmits a message tothe presence server 201 to inform the server of the presence of the lowpower transceivers 100 and 102. The connection to each low powertransceiver will be made prior to coordinated scheduling, but eachconnection may be established independently at any time withoutoccurring simultaneously with or in a fixed relationship to any otherconnection.

Regardless of the method of registration performed, be it as describedabove or by way of another technique, the wireless computing devices 220and 222 operating the low power transceivers 100 and 102 must be withina range suitable for receiving low power signals from and transmittinglow power signals to the host transceiver 212. This range will varybased upon the specific design characteristics of the low powertransceivers 100 and 102 and host transceiver 212. Since the messagespassed between the low power transceivers 100 and 102 and hosttransceiver 212 (e.g., acknowledgement messages) are transmitted overthe low power, low bandwidth, control channel, and not a primarycommunication channel (e.g. an 802.11 channel) the standard high powerNIC cards of the wireless computing devices 220 and 222 need not be usedfor facilitating the presence detection and registration process,resulting in less power usage by the devices. Also, because theregistration process is executed via a low power control channel ratherthan the high power channel, the wireless computing devices 220, 222operating the low power transceivers 100, 102 need not be powered upduring the registration.

In an embodiment of the invention, the low power control channel of anydevice may be idled during non-idle periods of operation by the wirelesscomputing devices 220 and 222 for reducing power consumption. Thus, forexample, when a standard wireless NIC card is active on a computingdevice for facilitating communication between the wireless computingdevice and the network 202, the low power transceiver 100 can be powereddown or placed into a nominal power mode (e.g., sleep mode of operation)wherein no transmissions or received signal processing is performed.Once the standard NIC of the wireless computing device is placed in alow power state of operation or becomes idle, the low power transceivercan be powered up to resume its normal operation on the device. In thisway, there is no substantial concurrent power usage by the wirelesscomputing device in maintaining both the standard NIC and the low powertransceiver in a powered up state.

When numerous wireless computing devices attempt to access the network202 via the access point 210, data transfer congestion often results.That is, when multiple wireless computing devices, such as devices 220and 222 contend for the bandwidth of the same access point, one or moredevices may experience unacceptable delay, or denial of service. In oneembodiment of the invention, illustrated by the flow chart in FIG. 5 andthe schematic illustrated in FIG. 7, multiple wireless computing devicesvying for communication bandwidth at an access point will have theiraccess to the channel for data transmission scheduled based upon controlinformation sent over their low power channel. This technique avoidswastage of the primary channel bandwidth caused by sending control andscheduling information over the primary channel.

Beginning at step 400, the wireless computing device registers with thebrick server in a fashion such as previously discussed or otherwise.After registering with the access point, the low power transceivertransmits control information to the host transceiver logicallyconnected to the access point, in step 402, informing the access pointthat the wireless computing device has data to transmit over the primarywireless channel. Types of control information include, but are notlimited to, data packet priority information, data packet transmissiondeadline information, channel access information, and the number of datapackets currently in a queue. Based upon this information and ascheduling algorithm, the access point, in step 404, generates a sortedlist of nodes having data packets to transmit and the packet priority ofeach packet. After generating this list, the access point then transmitsthe appropriate scheduling information, in step 406, to each contendinglow power transceiver to notify the wireless computing device as to whenit should send data over the primary channel through the standard NIC.Finally, in step 408, a wireless computing device proceeds to transmitthe primary data over the 802.11 channel according to the receivedscheduling information, while the other wireless computing devices vyingfor the channel stand by. The scheduling information may also comprise a“wake-up” signal notifying a wireless computing device to power up andthen to transmit data through the standard NIC. Such “wake-up” signalsmay be transmitted based upon the priority of the data on the listgenerated in step 404.

By placing the control information and scheduling information out ofband with respect to the data transmission, the invention conserves andbetter utilizes the primary channel bandwidth. The control informationand corresponding scheduling information is sent via the low powerchannel, whereas the useful data is sent via the primary channel.Therefore, true work conservation can result from proper work conservingalgorithms.

One of skill in the art will recognize that numerous schedulingalgorithms exist, any one or more of which can be used in conjunctionwith the present invention. Suitable scheduling algorithms include, butare not limited to, fair queuing and first come, first serve scheduling.Examples of fair queuing scheduling algorithms that can be used inconjunction with the present invention appear in S. Keshav, On theEfficient Implementation of Fair Queueing, Journal of Internetworking:Research and Experience, Volume 2, pages 27–73 (1991), hereinincorporated by reference in its entirety for all that it discloses.Additionally, one of skill in the art will recognize that while theexamples given above sometimes reference the 802.11 standard family ofprotocols, any communication protocols may be used to implement thepresent invention. Also note that although specific frequencies aregiven in the foregoing examples, any frequency that is supported in anysection of the world may be used as the frequency for data transmissionor control information transmission according to the present invention.Preferably, frequencies are used that are available internationally fordevices that may be used internationally, thus avoiding RF interferenceand channel failure.

In another embodiment of the present invention, the scheduler at theaccess point is in synchronization with a scheduled wireless computingdevice, allowing scheduling of primary channel access prior to poweringup the wireless network device. For example, if the access point andwireless computing device are rate synchronized, wherein the clocks ofeach count time at substantially the same rate, the access point cancoordinate with the wireless computing device to power up after passageof a specified interval so that the primary NIC can transmit or receivedata at that time. This is typically facilitated by use of a networktiming protocol (NTP), or any other suitable protocol, over the lowpower channel through a low power transceiver that is held constantlyready to receive and/or transmit data. One of skill in the art willrecognize that there are numerous other timing protocols andsynchronization technologies that will work within the present inventionto provide synchronized behavior.

Note that the low power control channel and the primary channelpreferably employ different frequencies. In one example, the low powertransceiver employs a carrier at 433 MHz or 915 MHz, while the standardNIC for the primary channel operates at 2.4 GHz. As discussed above, thelow power transceiver and the standard NIC have different power usagerequirements due in part to differences in frequency, data rate, andsignal strength.

In a further embodiment, the powering up of the low power transceiveritself can be scheduled. This embodiment utilizes precise clock ratesynchronization between the low power transceiver on a wireless deviceand the host transceiver located at the access point. When the low powertransceiver and the host transceiver have access to clocks running atessentially the same rate, neither the low power transceiver nor thestandard NIC need be maintained in a constantly active state. Forexample, when the low power transceiver has received an indication thattransmission from its host device will be permitted after a specifiedinterval, then both the low power transceiver and the standard NIC canbe placed in a non-active mode during that interval after accounting fora known start-up delay of each. Note that although the clocks of the lowpower transceiver and the host transceiver need not reference identicalrate clocks, the rates of both should be close enough that channelscheduling is not impacted by any inaccuracies to the extent that itresults in transmission collisions or other detrimental behavior.

In an alternative embodiment of the present invention, illustrated inFIG. 6, the aforementioned scheduling function is performed at a hostcomputer 206 containing a host transceiver 212, rather than at thewireless access point 210 itself. The host computer 206 may be connectedto the network 202 via the wireless access point 210 or otherwise. Thisnetworking environment is built in substantially the same way as theenvironment wherein the wireless computing devices are connecteddirectly to the access point 210. Note that in this or otherembodiments, it is not required that both the primary and low powerchannels connect the same nodes. Thus, with reference to FIG. 6, awireless device 220, 222 may communicate with the host computer 206 viathe low power channel while communicating directly with the access point210 via the primary (e.g. 802.11) channel.

While the invention is not limited to any particular radio range for thelow power channel, it is preferable that the low power transceiver ofthe wireless computing devices 220 and 222 be spatially close enough toa host transceiver enabled access point 210 during operation to ensureRF signal reception and data integrity. However, it is still possible tohave such low power communications even when the relevant low powertransceiver is not within direct communication range of the hosttransceiver 212 operating at the access point, or at a host computer.Techniques for facilitating out-of-range communication are discussed inthe following section of the detailed description.

In FIG. 8 a, a first wireless computing device 300 operating a low powertransceiver 302 and a second wireless computing device 304 operating asecond low power transceiver 306 are shown to be out of a suitabledirect range for supporting low power communication with an access point210 operating a host transceiver 308. As such, with respect to eachwireless computing device 300, 304, the low power transceiver 302,306 isunable to directly communicate with the access point 210. In accordancewith an embodiment of the invention, however, the first wirelesscomputing device 300 may be able to communicate with the access point210 using multi-hop networking, as illustrated in FIG. 8 b.Specifically, when a third wireless computing device 314 operating a lowpower transceiver device 316 is within range of the access point 210, alow power control channel 318 is established between the third computingdevice 314 and host transceiver enabled device 210.

When the third wireless computing device 314 is also within range ofanother wireless computing device 300, 304, the low power transceiveroperating on the wireless computing device 300, 304 establishes contactwith the third wireless computing device 314 via a low powercommunication channel. In particular, the low power transceiver 302, 306of the wireless computing device 300, 304 sends a message to the lowpower transceiver 316 of the third wireless computing device 314 forretransmission to the access point 210. The low power transceiver 316 ofthe third wireless computing device 314 then makes a determination as towhether to accept this request or not. If the request is accepted, acontrol channel is established between the third wireless computingdevices 314 and the other device 300, 304. The low power transceiver302, 306 associated with the out-of-range wireless computing device 300,304 sends a registration message to the third wireless computing device314 via the low power channel. This message is then forwarded by thethird wireless computing device 314 to the host transceiver 308operating at the access point 210, via the low power channel between thetwo. Once the registration of the low power transceiver 302, 306 of theout-of-range wireless computing device 300, 304 is recorded by theserver 310, the out-of-range wireless computing device 300, 304 is ableto engage in communication with other devices over the network 312.

Once the out-of-range wireless computing devices 300, 304 areregistered, either one may then transmit control information, such asbandwidth requests, through the third wireless network device 314 to thehost transceiver 308 at the access point 210, or host computer, aspreviously described above. Upon receiving the control information, theaccess point 210 applies a scheduling algorithm to all requestinformation in order to schedule channel access for multiple wirelessnetwork devices seeking use of the same high power channel. The accesspoint 210 then transmits the scheduling information through the hosttransceiver 308 to the third wireless network device 314 via a low powerchannel. When the scheduling information reaches the third wirelessnetwork device 314, it is forwarded to the pertinent out-of-rangewireless network device. For example, if the scheduling information isin the form of a “wake-up” signal, then it would only be transmitted tothe wireless device that is to be powered up in order to receive ortransmit data, i.e. the device that has access to the channel at thattime. If the scheduling information is in the form of a schedule ofchannel access of multiple wireless access devices, the schedulinginformation may be sent to any or all out-of-range devices as needed bythe third wireless device.

Those skilled in the art will recognize that the above-describedprocesses will often be carried out within an environment of more thantwo competing wireless computing devices although just two such devicesare illustrated herein. As will be appreciated by those skilled in theart, whenever a number of wireless computing devices are within anappropriate low power radio range of one another, multi-hopcommunication can ideally be engaged by an unlimited number of suchdevices. This is particularly advantageous in the case of mobilewireless computing devices, such as PocketPCs, wherein a directconnection to a host transceiver enabled host, such as access point 210,may be limited as the device user roams from one location to another.Note that although two low power jumps are used in the describedexamples to reach an out-of-range device, any number of such jumps maybe utilized without limitation. Furthermore, it is contemplated that oneor more out-of-range devices may need to use multi-hop connectivity,while another device or devices are either in direct range, or at leastrequire fewer hops.

In view of the many possible embodiments to which the principles of thisinvention may be applied, it should be recognized that the embodimentsdescribed herein with respect to the drawing figures are meant to beillustrative only and should not be taken as limiting the scope ofinvention. For example, those of skill in the art will recognize thatthe elements of the illustrated embodiments shown in software may beimplemented in hardware and vice versa or that the illustratedembodiments can be modified in arrangement and detail without departingfrom the spirit of the invention. Therefore, the invention as describedherein contemplates all such embodiments as may come within the scope ofthe following claims and equivalents thereof.

1. An access point for interfacing a plurality of wireless devices to anetwork comprising: an interface to a wireless channel for transmittingand receiving data over the first wireless channel, wherein the dataomits scheduling information related to scheduling access to the firstwireless channel; and an interface to a second wireless channel fortransmitting and receiving scheduling information, wherein thescheduling information comprises scheduling information related toscheduling access to the first wireless channel, wherein the interfaceto the first wireless channel consumes more power to transmit a bit onthe first wireless channel than the interface to the second wirelesschannel consumes to transmit a bit on the second wireless channel,wherein the scheduling information is derived based at least in part onthe number of packets waiting in a queue for transmission over the firstwireless channel.
 2. The access point according to claim 1, furthercomprising a network interface card comprising both the interface to thefirst wireless channel and the interface to the second wireless channel.3. The access point according to claim 1, wherein the schedulinginformation comprises data packet priority information.
 4. An accesspoint for interfacing a plurality of wireless devices to a networkcomprising: an interface to a wireless channel for transmitting andreceiving data over the first wireless channel, wherein the data omitsscheduling information related to scheduling access to the firstwireless channel; and an interface to a second wireless channel fortransmitting and receiving scheduling information, wherein thescheduling information comprises scheduling information related toscheduling access to the first wireless channel, wherein the interfaceto the first wireless channel consumes more power to transmit a bit onthe first wireless channel than the interface to the second wirelesschannel consumes to transmit a bit on the second wireless channel,wherein the scheduling information comprises data packet transmissiondeadline information.
 5. The access point according to claim 1, whereinthe first wireless channel and the second wireless channel employdifferent carrier frequencies.
 6. The access point according to claim 1,wherein the first wireless channel comprises an 802.11 basedcommunication channel.